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. 1980 Nov;66(5):835–837. doi: 10.1104/pp.66.5.835

Effects of Divalent Cations and Polyethylene Glycol on the Membrane Fluidity of Protoplast 1

Wendy F Boss 1, Ralph L Mott 1
PMCID: PMC440736  PMID: 16661536

Abstract

Calcium is often used to stabilize membranes and enhance membrane fusion. We have used the fatty acid spin label, 5-nitroxy stearic acid to measure fluidity changes in the plasma membrane of carrot suspension culture cell protoplasts in response to divalent cations. Electron spin resonance spectra from spin-labeled protoplasts showed no membrane fluidity changes (as determined by the hyperfine splitting constant, 2Amax) in the presence of Mg from 0 to 10 millimolar or Ca from 0 to 5 millimolar. Protoplasts in 10 millimolar Ca, however, showed a dramatic increase of 5 gauss in 2Amax and evidence of exchange-broadening. The original (control) spectrum was regained by removing bound Ca with a Ca chelator. Polyethylene glycol, which enhances protoplast fusion, did not alter the membrane fluidity in the region of the 5-nitroxy stearic acid probe if added simultaneously with or following 10 millimolar Ca. Pretreatment with polyethylene glycol did, however, inhibit the Ca-induced phase separation. These data on a living system describe membrane structural changes under conditions similar to those used for protoplast fusion.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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